In this study of the longitudinal course of the development of mastery motivation, the goals are to determine whether mastery motivation in infancy is predictive of latter mastery behavior and whether specific aspects of parent-infant interaction influence mastery behavior at 2 1/2 years. The interrelationships between the development of cognitive functions and mastery motivation during the preschool years is also being studied. Methods have been developed to assess similar aspects of mastery at 2 1/2 years as were studied at 6 and 12 months of age. Data are being collected using these measures of mastery, the McCarthy Scales, an observation of the infant's free play with the mastery toys, and a brief observation of mother-child interaction with another set of toys.